Separator for secondary batteries with enhanced stability and method of manufacturing the same

ABSTRACT

Disclosed are a separator for secondary batteries with enhanced stability and a method of manufacturing the separator. The separator can prevent self-discharge which may occur when a porous non-woven fabric material is used for a separator; can perform a shutdown function at a high temperature of 200° C. or less; and can avoid even under harsh conditions of high temperatures, deterioration in stability caused by internal short-circuit of positive and negative electrodes. In particular, the separator for secondary batteries of the present invention includes a porous non-woven fabric material impregnated with a baroplastic polymer powder and pores of the porous non-woven fabric material are filled with the baroplastic polymer powder by pressing an assembly of the secondary battery.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. § 119(a) the benefit of priorityto Korean Patent Application No. 10-2016-0178862 filed on Dec. 26, 2016,the entire contents of which are incorporated herein by reference.

BACKGROUND (a) Technical Field

The present invention relates to a separator for secondary batterieswith enhanced stability and a method of manufacturing the same. Theseparator for secondary batteries may prevent self-discharge, which mayoccur when a porous non-woven fabric material is used for a separator,and may perform a shutdown function at a high temperature of about 200°C. or less. Thus, even under harsh conditions of high temperatures,deterioration in stability caused by internal short-circuit of positiveand negative electrodes may be prevented.

(b) Background Art

The development and commercialization of electric vehicles have broughtabout increasing interest in secondary batteries with improved safety.As the safety of secondary batteries directly may be associated with thesafety of separators, separators with improved safety have beensubstantially studied and developed.

In order to secure stability of lithium secondary batteries, in additionto production of separator by a dry or wet method using a conventionalpolyolefin polymer, research has been focused on non-woven fabricseparators with improved heat resistance using other polymers. However,these non-woven fabric separators may have substantially large pores andthus may have a risk of self-discharge. When such non-woven fabricseparators are used, storage characteristics of secondary batteries maydeteriorate. In addition, non-woven fabric separators may have problemsof uneven or insufficient impregnation of electrolytes due to highporosity of non-woven fabric separators, as compared to separatorsproduced by conventional dry or wet methods. Moreover, non-woven fabricseparators produced using materials with excellent heat resistance mayexhibit excellent heat resistance, but a shutdown function may not besufficiently performed at high temperatures due to large pore size andhigh porosity, which may result in serious safety problems uponovercharging of secondary batteries.

Thus, there is a need for development of separators for secondarybatteries, which may inhibit self-discharge, exhibit improvedelectrolyte impregnation, perform the function of shutdown and thus mayprovide improved stability.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

In preferred aspect, the present invention provides a separatorsproduced by impregnating pores of a porous non-woven fabric materialwith a baroplastic polymer powder and pressing the porous non-wovenfabric material upon assembly of a secondary battery such that the poresof the porous non-woven fabric material may be filled with thebaroplastic polymer powder. As such, self-discharge of the secondarybattery including the separator of the invention may be avoided, ashutdown function may be provided at a high temperature of about 200° C.or less and an internal short-circuit may be prevented.

In one aspect, the present invention provides a separator for secondarybatteries with enhanced stability. The separator for secondary batterieswith enhanced stability may include a porous non-woven fabric material;and a baroplastic polymer powder impregnated in the porous non-wovenfabric material. In particular, pores in the porous non-woven fabricmaterial may be filled with the baroplastic polymer powder by pressing.

The term “baroplastic” or “baroplastic polymer”, as used herein, refersto a polymeric material that can change in phase or morphology thereofwhen a pressure is applied, for example, by exhibiting increasedfluidity or flow of the material, with or without applying heat orthermal energy. For instance, the baroplastic material or polymer may bea rigid or rubbery solid under ambient condition but may flow or havefluidity when the pressure is applied.

In particular, the pores of a porous non-woven fabric material may beimpregnated with a baroplastic polymer powder and pores of the porousnon-woven fabric material may include the baroplastic polymer powder. Inparticular, the pores may be filled with the baroplastic polymer powderby pressing, for example, upon assembly of a secondary battery.

Preferably, the porous non-woven fabric material may include one or moreselected from the group consisting of polyolefin, polyimide, aramid,cellulose, polyacrylonitrile, polyester and polyamide.

The pores of the porous non-woven fabric material may suitably have asize of about 1 μm to 100 μm and the porous non-woven fabric materialmay suitably have porosity of about 20% to 70%.

The baroplastic polymer powder may include one or more selected from thegroup consisting of polystyrene, polyisoprene, poly(n-butyl acrylate),2-ethylhexyl acrylate, poly(pentyl methacrylate), poly(butylmethacrylate), polycarbonate, poly(methyl methacrylate), poly(vinylchloride), poly(ethyl acrylate), poly(ethyl methacrylate), andpolybutadiene.

The baroplastic polymer powder may suitably have an average particlediameter of about 10 to 100 μm.

The pressing the assembly of the secondary battery may be suitablycarried out by hot-pressing at a temperature of about 20° C. to 100° C.and a pressure of about 1 to 4 ton/in².

The separator for the secondary battery may further include a coatinglayer of a binder solution formed on surfaces of the porous non-wovenfabric material impregnated with the baroplastic polymer powder therebypreventing detachment of the baroplastic polymer powder. In particular,the binder solution may include i) at least one binder selected from thegroup consisting of polyvinylidene fluoride (PVdF), polyester andpolyacrylonitrile; and ii) N-methyl-2-pyrrolidone (NMP) orN,N-dimethylacetamide (DMAc).

The term “binder”, as used herein, refers to a polymeric resin orpolymeric compound that may provide adhesion to a substrate or coatinglayer on a substrate. The binder may be cured, dried, hardened orpolymerized by heat, UV, cross-linking agent, chemical additives,electron beams, or the like.

In another aspect, the present invention provides a method ofmanufacturing a separator for secondary batteries with enhancedstability. The method may include: (a) impregnating a porous non-wovenfabric material with a baroplastic polymer powder; (b) coating surfacesof the baroplastic polymer powder-impregnated porous non-woven fabricmaterial using a binder solution, (c) drying the coated porous non-wovenfabric material, and (d) laminating a positive electrode and a negativeelectrode on the dried porous non-woven fabric material to form anassembly and pressing the assembly.

The term “assembly”, as used herein, refers to an assembly including atleast one or more components of a secondary battery. Preferably, theassembly of the present invention may include a positive electrode, aseparator and a negative electrode. For instance, the assembly of thepresent invention may include the positive electrode attached to a firstside of the separator, the negative electrode attached to a second sideof the separator, and the separator. Preferably, the assembly of thepresent invention may be formed by laminating the positive electrode andthe negative electrode to each side of the separator and pressing thesame, for example, by hot pressing at elevated temperature and pressureconditions.

The porous non-woven fabric material may include one or more selectedfrom the group consisting of polyolefin, polyimide, aramid, cellulose,polyacrylonitrile, polyester and polyamide.

Preferably, pores of the porous non-woven fabric material may have asize of about 1 μm to 100 μm and the porous non-woven fabric materialmay have porosity of about 20% to 70%.

The baroplastic polymer powder may suitably include one or more selectedfrom the consisting of polystyrene, polyisoprene, poly(n-butylacrylate), 2-ethylhexyl acrylate, poly(pentyl methacrylate), poly(butylmethacrylate), polycarbonate, poly(methyl methacrylate), poly(vinylchloride), poly(ethyl acrylate), poly(ethyl methacrylate), andpolybutadiene.

The baroplastic polymer powder may suitably have an average particlediameter of about 10 to 100 μm.

In step (d), the pressing may be carried out by hot-pressing at atemperature of about 20° C. to 100° C. and at a pressure of about 1 to 4ton/in².

The binder solution for the coating in the step (b) may be prepared bydissolving at least one binder selected from the group consisting ofpolyvinylidene fluoride (PVdF), polyester and polyacrylonitrile inN-methyl-2-pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc).

Further provided is a secondary battery including the separator asdescribed herein.

Still further provided is a vehicle including the secondary battery asdescribed herein.

Other aspects and preferred embodiments of the invention are discussedinfra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present invention, and wherein:

FIG. 1A shows a cross-section of a conventional porous non-woven fabricmaterial and FIG. 1B shows a cross-section of an exemplary porousnon-woven fabric material impregnated with an exemplary baroplasticpolymer powder (left), and a cross-section of an exemplary porousnon-woven fabric material impregnated with an exemplary baroplasticpolymer powder after pressing (right), according to an exemplaryembodiment of the present invention;

FIG. 2 shows an exemplary separator produced by hot pressing the porousnon-woven fabric material impregnated with the baroplastic polymerpowder according to an exemplary embodiment of the present invention;and

FIG. 3 is a graph showing a charge/discharge curve of an exemplarysecondary battery from the results of Table 1.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularexemplary embodiments only and is not intended to be limiting of theinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about.”

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

Hereinafter, various aspects of the present invention will be describedin more detail.

In order to inhibit self-discharge and perform the function of shutdownat a high temperature of 200° C. or less, the present invention providesa separator for secondary batteries with enhanced stability. Inparticular, the separator may include a porous non-woven fabric materialcontaining pores and impregnated with a baroplastic polymer powder. Thepores in the porous non-woven fabric material may be filled with thepowder by pressing upon assembly of a secondary battery.

In an exemplary embodiment, the porous non-woven fabric materialaccording to the present invention may have a melting point of about200° C. or greater to impart high heat resistance. In particular, theporous non-woven fabric material may include one or more selected fromthe group consisting of polyolefin, polyimide, aramid, cellulose,polyacrylonitrile, polyester and polyamide. The non-woven fabricmaterial may have pores having a size of about 1 μm to 100 μm and mayhave porosity of about 20% to 70%. Any porous non-woven fabric materialused in the related arts may be used without limitation thereto.

However, the porous non-woven fabric material may result inself-discharge due to non-uniform and large pore size and high porosity,thereby causing deterioration in storage characteristics and electrolyteimpregnation characteristics of secondary batteries. In addition,shutdown function may not be performed at high temperatures.

Accordingly, the present invention may solve the problems ofconventional non-woven fabric separators by impregnating the non-wovenfabric with the baroplastic polymer and molding the same.

According to an exemplary embodiment of the present invention, thebaroplastic polymer impregnated in the pores of the porous non-wovenfabric material may have miscibility of the block copolymer blends,e.g., polystyrene and polyisoprene, as being in the porous non-wovenfabric material at a temperature of 90° C. or less, the baroplasticpolymer impregnated in the pores of the porous non-woven fabric materialmay close pores of the separator at high temperatures to perform ashutdown function.

The baroplastic polymer may include one or more selected from the groupconsisting of polystyrene, polyisoprene, poly(n-butyl acrylate),2-ethylhexyl acrylate, poly(pentyl methacrylate), poly(butylmethacrylate), polycarbonate, poly(methyl methacrylate), poly(vinylchloride), poly(ethyl acrylate), poly(ethyl methacrylate) andpolybutadiene. In particular, the baroplastic polymer may be a blockcopolymer of polystyrene and polyisoprene which may provide advantagessuch as formability at room temperature, formability at a low pressureand possibility of commercialization. Furthermore, the baroplasticpolymer may be used in an amount of 15 to 60% by volume, or particularlyin an amount of 20 to 50% by volume with respect to the volume of theporous non-woven fabric material. When the content of the baroplasticpolymer is less than about 15% by volume, with respect to the volume ofthe porous non-woven fabric material, the baroplastic polymer may not besufficient to fill pores of the non-woven fabric material duringpressing and molding processes. When the content of the baroplasticpolymer is greater than about 60% by volume the baroplastic polymer maycover surface pores of the non-woven fabric material. Accordingly, thebaroplastic polymer may be included or impregnated in the amount withinthe range defined above.

Furthermore, large pores of the porous non-woven fabric material may beimpregnated with the baroplastic polymer, such that the particles of thebaroplastic polymer powder may be smaller than large pores present inthe non-woven fabric material and may be greater than small porespresent therein. Accordingly, in an exemplary embodiment of the presentinvention, the baroplastic polymer powder may have an average particlediameter of about 10 to 100 μm. When the average particle diameter isless than about 10 μm, the baroplastic polymer powder may notsufficiently fill large pores of the non-woven fabric separator, andwhen the average particle diameter is greater than about 100 μm, thebaroplastic polymer powder may not sufficiently impregnate pores of thenon-woven fabric separator. The baroplastic polymer may have the size ordiameter within the range defined above.

In an exemplary embodiment, the pores of the non-woven fabric separatormay be filled with the baroplastic polymer powder by impregnation andsurfaces or both surfaces of the porous non-woven fabric materialimpregnated with the baroplastic polymer powder may be coated with abinder solution to improve bonding strength between the pores and thepowder.

The binder solution may be obtained by dissolving at least onenon-aqueous binder in a solvent. The non-aqueous binder may include, butnot be limited thereto, one or more selected from the group consistingof polyvinylidene fluoride (PVdF), polyester and polyacrylonitrile. Thesolvent may be N-methyl-2-pyrrolidone (NMP) or N,N-dimethylacetamide(DMAc). For instance, the binder solution may be a solution of PVdFdissolved in NMP.

According to an exemplary embodiment, the porous non-woven fabricmaterial may be impregnated with the baroplastic polymer powder to fillpores of the non-woven fabric material with the powder and the pores maybe filled with the powder by pressing the assembly of the secondarybattery.

For instance, a positive electrode and a negative electrode may belaminated on each side of the porous non-woven fabric materialimpregnated with the baroplastic polymer powder and then may be pressedby hot-pressing. The pressing may be carried out at a temperature ofabout 20° C. (room temperature) to about 100° C. and at a pressure ofabout 1 to 4 ton/in². When the pressing temperature is greater thanabout 100° C., the electrode and separator may be damaged. Thus, thepressing may be carried out at the temperature within the range definedabove. In addition, when the pressing pressure is less than about 1ton/in², the formability of the baroplastic polymer may deteriorate, andwhen the pressing pressure is greater than about 4 ton/in², electrodeedges may be detached. Accordingly, the pressing may be carried out atthe pressure within the range defined above.

In another aspect, the present invention provides a method ofmanufacturing a separator for secondary batteries with enhancedstability. The method may include: (a) impregnating a porous non-wovenfabric material with a baroplastic polymer powder; (b) coating surfacesof the porous non-woven fabric material impregnated with the baroplasticpolymer powder using a binder solution, (c) drying the porous non-wovenfabric material coated with the binder solution, and (d) laminating apositive electrode and a negative electrode on the dried porousnon-woven fabric material and pressing the positive electrode, thenegative electrode, and the porous non-woven fabric material by ahot-pressing process. In an exemplary embodiment, the positive electrodeand the negative electrode may be attached on each side of the driedporous non-woven fabric material.

In an exemplary embodiment, in the step (a), the porous non-woven fabricmaterial may be impregnated with the baroplastic polymer powder. Forinstance, the baroplastic polymer powder may be impregnated byfiltration.

The porous non-woven fabric material may be one or more selected fromthe group consisting of polyolefin, polyimide, aramid, cellulose,polyacrylonitrile, polyester and polyamide. The porous non-woven fabricmaterial may contain pores having a size of about 1 μm to 100 μm and mayhave a porosity of about 20% to 70%. Any porous non-woven fabricmaterial used in the related arts may be used without limitationthereto.

As described above, the baroplastic polymer may include one or moreselected from the group consisting of polystyrene, polyisoprene,poly(n-butyl acrylate), 2-ethylhexyl acrylate, poly(pentylmethacrylate), poly(butyl methacrylate), polycarbonate, poly(methylmethacrylate), poly(vinyl chloride), poly(ethyl acrylate), poly(ethylmethacrylate), and polybutadiene. In particular, the baroplastic polymermay be a block copolymer of polystyrene and polyisoprene to impartformability at room temperature, formability at a low pressure andcommercialization. Furthermore, as described above, the baroplasticpolymer may be used in an amount of about 15 to 60% by volume, orparticularly, in an amount of about 20 to 50% by volume, with respect tothe volume of the porous non-woven fabric material.

The baroplastic polymer powder may have an average particle diameter ofabout 10 to 100 μm. When the average particle diameter is less thanabout 10 μm, the baroplastic polymer powder may not sufficiently filllarge pores of the non-woven fabric separator, and when the averageparticle diameter is greater than about 100 μm, the baroplastic polymerpowder may not sufficiently impregnate pores of the non-woven fabricseparator. The average particle diameter of the baroplastic polymer maybe within the range defined above.

In an exemplary embodiment, in the step (b), surfaces of the porousnon-woven fabric material impregnated with the baroplastic polymerpowder may be coated with a binder solution to improve bonding strengthbetween the porous non-woven fabric material and the impregnatedbaroplastic polymer powder.

The binder solution may be obtained by dissolving at least onenon-aqueous binder in a solvent. The non-aqueous binder may be selectedfrom the group consisting of polyvinylidene fluoride (PVdF), polyesterand polyacrylonitrile and the solvent may be, but not limited thereto,N-methyl-2-pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc). Forinstance, the binder solution may include PVdF dissolved in NMP.

The coating of the separator may be carried out by various coatingmethods including dip coating, die coating and comma coating, and thecoating method in the related arts may be used without limitation. Forinstance, the binder solvent may be coated on one surface of thenon-woven fabric material impregnated with the baroplastic polymerpowder and dried, and subsequently the other surfaces thereof may becoated and dried. Alternatively, the binder solvent may besimultaneously coated on both surfaces of the separator and then dried.The drying may be carried out at a temperature of about 80° C. to 120°C.

In an exemplary embodiment of the present invention, in the step (d), apositive electrode and a negative electrode may be attached or laminatedon the dried porous non-woven fabric material and pressed, for example,by a hot-pressing process, which may be important for filling pores ofthe porous non-woven fabric material. For instance, by the pressingstep, the baroplastic polymer powder may be prevented from beingseparated from the porous non-woven fabric material and bonding strengthbetween the separator and the electrode may be improved. The separatormanufactured by the method may be inserted or positioned between thepositive electrode and the negative electrode to produce a lithiumsecondary battery.

The hot-pressing may be carried out at room temperature (e.g., about 20°C.) to a temperature of 100° C. and a pressure of about 1 to 4 ton/in².When the pressing temperature is greater than about 100° C., theelectrode and the separator may be damaged. Thus, the pressing may becarried out at the temperature within the range defined above. When thepressing pressure is less than about 1 ton/in², the baroplastic polymermay not be sufficiently formed, and when the pressing pressure isgreater than about 4 ton/in², electrode edges may be detached. Thus, thepressing may be carried out at the pressure within the range definedabove.

In general, commercially available secondary batteries may explode whenexposed to high temperatures or heat of 200° C. or greater. In order tosecure safety of secondary batteries, equipment for preventing thetemperature of the battery from increasing to 200° C. or higher may berequired.

The separator manufactured according to the present invention may have ashutdown function by closing separator pores at a high temperature ofabout 200° C. or less. As described herein, the term “shutdown” refersto an operation that fine pores of the separator are blocked at hightemperatures. The shutdown of the separator under the conditions, suchas over-charging, allowing secondary batteries to be heated to hightemperatures, may improve safety features of the secondary battery bysuppressing additional heating.

Hereinafter, the present invention will be described in more detail withreference to examples. However, the examples are provided only forillustration of the present invention and the scope of the presentinvention is not limited to the examples.

EXAMPLE Comparative Example 1: Case of Using Porous Non-Woven FabricSeparator (Conventional)

A secondary battery was produced using a porous non-woven fabricseparator including 50% by weight of polyacrylonitrile (PAN) and 50% byweight of cellulose, an NCM-based positive electrode and a graphitenegative electrode.

Comparative Example 2

A secondary battery was produced using a porous non-woven fabricseparator including 50% by weight of aramid and 50% by weight ofcellulose, an NCM-based positive electrode and a graphite negativeelectrode.

Example 1

A porous non-woven fabric material including 50% by weight ofpolyacrylonitrile (PAN) and 50% by weight of cellulose was impregnatedby filtration with 50% by volume of a block copolymer of polystyrene andpolyisoprene as a baroplastic polymer powder, and the porous non-wovenfabric material was coated with a PVdF binder solution and was thendried at a temperature of 100° C. for one hour. Then, a positiveelectrode including an NCM-based active material, a graphite negativeelectrode and the dried porous non-woven fabric material were laminatedand then hot-pressed at a temperature of 50° C. and at a pressure of 1.5ton/in² to produce a secondary battery.

Test Example: Testing Confirming Stability Improvement

Inhibition of self-discharge and presence of shutdown function weremeasured for secondary batteries produced in Examples and ComparativeExamples and results are shown in Table 1 and FIG. 3.

(1) Method of measuring self-discharge inhibition: secondary batterieswith a capacity of 2 Ah, produced in Examples and Comparative Exampleswere charge/discharged once at 45° C., 2.5 to 4.2 V, and 1 A (0.5 C).

(2) Method of measuring shutdown function: overcharge testing wascarried out by charging secondary batteries with a capacity of 2 Ahproduced in Examples and Comparative Examples at a current density of 4A (2 C) and 12V, and measuring surface temperature and voltagevariations thereof.

TABLE 1 Overcharge temperature Items Self-discharge (max) Example 1 X 78° C. PAN/CL-PI/PS Comparative Example 1 ◯ 151° C. PAN/CL ComparativeExample 2 ◯ 204° C. AR/CL

FIG. 3 shows a charge/discharge graph showing self-discharge results ofTable 1. As can be seen from results of FIG. 3, Comparative Exampleusing a conventional non-woven fabric separator exhibited abnormalcharge behaviors due to self-discharge, while Example according to thepresent invention exhibited normal charge/discharge behaviors.

In addition, a battery using the baroplastic polymer-impregnatednon-woven fabric separator as in Example according to an exemplaryembodiment of the present invention exhibited a lower battery surfaceheating temperature upon overcharge than that of a battery producedusing a conventional non-woven fabric separator.

Upon overcharge, the baroplastic polymer partly melted and thus closedpores of the non-woven fabric separator to prevent an internalshort-circuit.

Accordingly, the separator with improved safety according to anexemplary embodiment of the present invention may inhibit self-dischargeand perform a shutdown function in which pores of the separator may beblocked at a high temperature of 200° C. or less and may be thus widelyused for secondary batteries.

As shown in the above description, the present invention may provide thefollowing effects.

Firstly, pores of a porous non-woven fabric separator may be impregnatedwith a baroplastic polymer and then molded to fill large pores of thenon-woven fabric material with the polymer, thereby inhibitingself-discharge of the non-woven fabric separator and improving roomtemperature and high-temperature storage characteristics of secondarybatteries.

Secondly, the large pores of the porous non-woven fabric separator maybe filled with the baroplastic polymer powder, thereby reducingdifference in pore sizes and improving electrolyte impregnationproperty.

Thirdly, the baroplastic polymer impregnated in pores of the porousnon-woven fabric separator may perform a shutdown function of blockingpores of the separator at high temperatures.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A method of manufacturing a separator for asecondary battery, comprising: (a) impregnating of a porous non-wovenfabric material with a baroplastic polymer powder by filtration; (b)coating surfaces of porous non-woven fabric material impregnated withthe baroplastic polymer powder using a binder solution; (c) drying thebinder solution-coated on the porous non-woven fabric material; and (d)laminating a positive electrode and a negative electrode on the driedporous non-woven fabric material to form an assembly and pressing theassembly, wherein the baroplastic polymer powder is molded by pressing,and wherein pores in the porous non-woven fabric material are filledwith the baroplastic polymer by molding the baroplastic polymer powder,wherein the pressing is carried out by hot-pressing at a temperature ofabout 20° C. to 100° C. and at a pressure of about 1 to 4 ton/in²,wherein the baroplastic polymer powder comprises block copolymer ofpolystyrene and polyisoprene, wherein the baroplastic polymer powder hasan average particle diameter of about 10 to 100 μm, and wherein anamount of the baroplastic polymer powder is 15% by volume to 60% byvolume based on the volume of the porous non-woven fabric material. 2.The method according to claim 1, wherein the porous non-woven fabricmaterial comprises one or more selected from the group consisting ofpolyolefin, polyimide, aramid, cellulose, polyacrylonitrile, polyesterand polyamide.
 3. The method according to claim 1, wherein pores of theporous non-woven fabric material has a size of about 1 μm to 100 μm andthe porous non-woven fabric material has porosity of about 20% to 70%.4. The method according to claim 1, wherein the binder solution isprepared by dissolving at least one binder selected from the groupconsisting of polyvinylidene fluoride (PVdF), polyester andpolyacrylonitrile in N-methyl-2-pyrrolidone (NMP) orN,N-dimethylacetamide (DMAc).